Stiffness Optimization And Design Of Connectors For Very Large Floating Structure

As a unique type of ocean engineering equipment,Very Large Floating Structure(VLFS)aims at the national strategic demands in naval defense and ocean resource development.Due to its large size,meanwhile considering the security of structures and the feasibility of construction,transportation and deployment,it is usually designed into a multi-modular type,in which modules are coupled by flexible connectors.The connectors are the most important parts for the whole system.An appropriate stiffness configuration of connectors contributes to improve stability of systems and survival ability in rough sea,which is also a prerequisite before the prototype design of connectors.Based on VLFS,a general strategy is proposed to resolve the optimum stiffness configuration for flexible connectors,which is utilized as a theoretical guideline for the structural design of flexible connectors.According to linear wave theory,a dynamic model of a multi-module floating system is established by utilizing the Rigid-Module-Flexible-Connector model where flexible connectors are treated as linear springs in three translational directions.Then the characteristic of connector stiffness is investigated,which could provide theoretical reference for subsequent stiffness optimization.Regarding design purposes,designers wish to achieve a relatively stationary state in the responses of floating modules for requirements of specific engineering applications.Meanwhile connector loads are also expected to be as small as possible to ease the difficulty of the prototype design of the connector and to enhance the safety and reliability of the system.However,the responses and loads are usually in conflict.Obviously,it is a typical multi-objective optimization problem.The linear weighted sum method and genetic algorithm are combined to establish a routine procedure for floating airports consisting of different number of modules,and the optimum stiffness configurations in different sea conditions are investigated by numerical experiments.The results indicate that the combination of small longitudinal stiffness,large transversal and large vertical stiffness is most favorable for systems.Compared with rigid hinge connectors,connectors with optimum stiffness configurations have better performance.Based on the optimization results,recommendable range of connector stiffness is investigated for guideline of structural design.Based on the recommendable range of connector stiffness,a novel type of connector with optimum stiffness configuration is proposed for a three-module floating system.By utilizing finite element method,the stress,deformation,stiffness and structural strength are analyzed and verified.As an application of connector stiffness optimization,it reveals the technological feasibility of the optimization strategy.Presently,there are few studies about stiffness arrangement for flexible connectors.In this thesis,a general optimization procedure is proposed for optimum stiffness configuration,in which engineering requirements,wave conditions and other factors are taken into consideration.It can be applied for different floating systems under complex ocean environment.Also,a novel flexible connector based on optimum stiffness configuration is proposed which can be used for connection of VLFS.